In the official rules, Hobart's Funnies may ignore movement restrictions of beach, march and wire (bobbin) or ford and trench (fascine). Railroad always stops movement.

I am designing a scenario with Hobart's Funnies and railroad, which could be ignored by armor equipped with proper accessory. But which one? I don't really understand how bobbin and fascine work, so could somebody explain them a little and suggest a realistic option? (Scenario-specific special rule.)

A BOBBIN had a reel on it with meshed fabric. This was laid out over sand or marshy ground in order to allow the tank to gain traction where it might be able to move. Once the fabric was laid it formed a temporary roadway for other vehicles.

The FASCINE was a bundle of timber carried on an armored vehicle. It was primarily meant to fill a trench or tank trap that could not be crossed because of its depth. The FASCINE bundle was dropped into the hole or trench allowing the tracked vehicle to move over top of it. Sometimes it took more than one bundle to fill a hole or trench.

I don't know if there was any accessories that allowed for quicker movement over railways.

I will try to answer to your question.
Hobart's Funnies were conceived to facilitate landing operations for the liberation of Europe, that means the Normandy landings.
Each funny tank had its own function against a particular obstacle but no one was conceived to cross railroad.
The only one you can use to cross railroad easily is (in the equipment pack) the Assault Bridge. But remember that it was conceived to cross ditches or trenches but not railroad.

So neither bobbin nor fascine really fits as representative "railroad-crosser". The railroad still plays a major role in the scenario, so I'll try and see if bridge could be used. I think I'll use the rules for bridge first, and if that doesn't work, let the Churchills just ignore railroad hexes.

I seriously doubt that railroad tracks impeded tank travel in real life to the degree modeled in M'44 if at all. So bear that in mind. I'm sure someone will disagree.

Railway tracks on the flat - like at a road crossing - might not impede tanks, but consider how railways are usually built on embankments for there is only a gradual change in gradient. A railway embankment or cutting would indeed impede tanks.

Well I for sure am no tank or railroad expert, and I have read of tanks having problems with some embankments and not with others. I find it hard to believe that (as a general rule) a single obstacle (lets say in non-urban area) warrants the complete stoppage of the unit as is the case with a forest or built-up area, because in those areas there are many obstacles.

That's why I think the affect should not necessarily be equivalent to a forest or town hex, i.e., its a matter of degree of affect in M44. I would have to research the issue to be convinced the impact is that large (but I won't because I'm not that interested, but maybe the OP will).

In any case, this is a rule that can probably be modified by special rules based on the historical circumstances, more so than other terrain types, particularly if you know the railroad did not actually impeded movement that much.

The reason I brought this up was because I wanted to hear some opinions on different accesories, and I was also wondering if fascine could be a reasonable option (I let the commander choose the accessories, just like in the EP scenario book) for, say, mine digger and petard mortar.

Lots of interesting conversation about armor and railroad in general. I changed the name of the topic.

If railroad affected armor movement like Sgt Storm suggested, it would be like beach hexes, wouldn't it? That makes the improvement/house-rule even better and maybe more realistic without complex new applications.

From what I have seen of railroad tracks, some ares would inhibit, if not prohibit armor movement.

This was true of the largest tank battle of Kursk where the RR embankment was 18' high and very steep. Tanks could not cross the RR tracks and it divided up the battlefield.

Different tanks of WW II had different abilities and had there limitations. I rememeber seeing a side by side performance test between a Panther and a Lee tank. Both tried to climb a 3' high wooden wall but the Lee could not due to lack of traction and or power.

Too steep a RR slope and /or the usual loose material found around RR tracks (ballast rocks) could pose a problem for many tanks.

A notable excetion was the Churchill tank which was put to good use in Tunisia. It could climb up the many steep slopes which were found there.

Other areas, like those found in RR yards and low embankment areas may slow them down a bit, but not force a stop.

Perhaps there should be two RR terrain types to reflect this difference.